What is Friction?

Have you ever slid an object like a wood block across a table? If you have, you probably know that the block will slow down before coming to a complete stop. Now, what would happen if you slid that same block on a material like ice? Would it slow down and eventually stop? No, it would continue sliding until it crashed into some obstacle like a tree or you intentionally stopped it. For these everyday examples, you can thank friction.

Friction is a force like gravity. This means it can pull or push on an object. It does not pull you down to the ground though like gravity. Instead, kinetic friction resists the motion of any moving object. Most common surfaces like carpet and wood are not completely smooth. You will probably see a lot of unevenness, which will only be magnified at the microscopic level. It is this roughness that causes an object to slow down as it rubs against any given surface.

But not all materials are the same in terms of how rough they are. Some materials such as wood or stone are much rougher than say ice. This why objects will slow down faster when slid across the pavement versus your local ice rink. Friction also applies to objects at rest. Static friction allows you to stand or sit in one place without sliding. In fact, static friction is the reason you are able to walk without constantly falling.

Finally, friction is affected by the variables: the mass of an object and roughness of a subject. If you want to impress those around, this roughness is known as the static friction coefficient (for stationary objects) and kinetic friction coefficient (for moving objects).

Now you have taken a step closer to fully understand the mysterious forces guiding our universe.

Friction Experiment

Picture Source: umsl.edu